You're not clear but I think you've got the SSD in one server, sharing it to the others via some form of network share - is that right?
If that's the case then unless it's one hell of a SAN the SSD will be significantly faster in terms of both latency and throughput for the server that contains the SSD. The other machines getting at this data over the network will be limited by that network link and the sharing capabilities of the machine with the SSD - even with the fastest network setup this will be much slower than the SSD and is likely to be much slower than a SAN.
So if my assumption about your usage is right then you'll have one very quick server and two much slower servers (if they do perform a lot of disk work anyway, it's irrelevant if not).
If you do a lot of disk work and want consistent performance then moving to a SAN will help with that, no single server is likely to have quicker disk access than another - and it's likely to be perfectly adequate for most needs too.